Secondary and micronutrients forms,availability and dynamics with factors affecting availability, chelation illustrations, appropriate pictures and cycles for all nutrients.

1. SECONDARY AND
MICRONUTRIENTS-
FORMS,AVAILABILITY AND
DYNAMICS
P R E S E N T E D B Y,
K A R T H E K A T.
2 0 1 9 5 3 1 0 0 2

2. ESSENTIAL ELEMENTS
• Plants need 17 elements for their growth and completion of life cycle
• They are carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium,
calcium, magnesium, sulphur, iron, manganese, zinc, copper,
boron, molybdenum, chlorine and nickel
• In addition, four more elements viz., sodium, cobalt, vanadium and
silicon are absorbed by some plants for special purposes (beneficial
elements).
• Plants require these elements in varied proportions

3. SECONDARY & MICRONUTRIENTS
• Macro nutrients- Required in larger quantities compared to other mineral
nutrients.
– Primary nutrients: N, P, K - required in high amounts
– Secondary nutrients: Ca, Mg, S – required in comparatively lower
amount than primary
• Micro nutrients- Required in trace quantities.
– Fe, B, Zn, Cu, Mo, Mn, Co, Ni

4. SECONDARY NUTRIENTS
The essentiality of the secondary nutrients Ca, Mg and S was given by Carl
Sprengel (1839)
• Calcium- Cell growth and division, component of cell wall, promotes the
development of the root system and the ripening of fruit and seeds, found in
the growing parts of plant (apex and buds).
• Magnesium-Component of chlorophyll, enzyme activation, fruit ripening, seed
germination, reinforces cell walls and promotes the absorption of phosphorous,
nitrogen and sulphur by plants
• Sulphur- Formation of amino acids and proteins, component of several
proteins, enzymes and vitamins, contributes to chlorophyll production and
helps plants absorb potassium, calcium and magnesium.

5. UPTAKE FORM & MOBILITY
Mobility in Soil:
The mobile nutrients are highly soluble and are not adsorbed on clay
complex; e.g.: SO4
- ,SO4
2-
Less mobile nutrients are also soluble, but they are adsorbed on
clay complex and so their mobility is reduced; e.g.: Ca+ and Mg2+
Mobility in Plants:
A mobile nutrient in the plant, moves to the growing points in case of
deficiency. Immobile nutrient do not move to growing points during
deficiency.

6. CALCIUM
• The important source of calcium in mineral soils are,
– Anorthite
– Calcite
– Dolomite
– Gypsum
• Factors affecting Ca2
+ availability
1. Total Ca supply: Sandy and acidic soils with low CEC have less Ca.
2. Soil pH: In acid soils Ca is not readily available to plants at low concentration.
3. CEC: Soils having low CEC might will supply more Ca2
+
4. % Ca saturation: High saturation Ca2
+ indicates favourable pH for plant growth and
microbial activity.
5. Type of soil colloid: 2 : 1 type require higher Ca saturation than 1: 1 type.
6. Ratio of Ca2
+ to other cations: Increasing the Al3 + conc. in soil solution reduces Ca
uptake in plant.

7. CALCIUM DYNAMICS IN SOILS
In acid and humid region soils, Ca occurs largely in exchange form and as
primary minerals. In most of these soils Ca2
+, Al3 + and H+ dominates the exchange
complex. The forms of Ca are
1)Solution Ca2
+
2)Exchangeable Ca
3)Mineral Ca
• The activity of solution Ca is decreased by leaching or plant removal.
• If solution Ca is decreased, the equilibrium shifts in the opposite direction with
subsequent desorption of some of the Ca2+ by the exchange complex.
• It may be (a) lost in drainage H2O.
(b) absorbed by organisms
(c) adsorbed on the CEC
(d) reprecipitated as secondary calcium compound.

9. MAGNESIUM
Sources of soil Magnesium
• In arid region- Epsomite (Mg SO4 7H2O)
• Primarily minerals-Biotite, Dolomite, Hornblende, Olivine, Serpentine.
• Secondary minerals (a) Chlorite (b) Illite (c) Montmorillonite.
Forms and availability of Mg in the soil
• 1. It occurs predominately as exchange and solution mg.
• 2. Coarse textured soil exhibits the greatest potential for Mg deficiencies.
• 3. Competition between NH4+ and Mg2+ also lower the Mg2+ availability to crops.
• Magnesium is absorbed
as Mg2
+
• Concentration in crop
varies between 0.1 and
0.6%
• Taken by plant by Mass
flow and diffusion.

10. Dynamics of Magnesium
• Magnesium is available to plants due to weathering of biotite, dolamite,
chlorite, serpentine and olivine.
• The released magnesium may be absorbed by plants and microorganisms,
lost in drainage or re-precipitated as secondary minerals.
• Magnesium in soil solution and exchangeable form are in dynamic
equilibrium, similar to calcium.
• When plant takes, concentration in soil solution decreases and so Mg ions
are released into soil solution.
• It is leached and depends on the Mg content, rate of weathering, intensity of
weathering and uptake of plants.

12. SULPHUR
Sources
• Sulphur bearing minerals Gypsum – CaSO4 2 H2O.
Epsomite – MgSO4, 7H2O
Mirabilite – Na2 SO4 , 10 H2O.
Pyrite – FeS2, Plutonic rocks
Forms of sulphur in soil
• Present both organic (90%) and Inorganic forms.
• The inorganic forms are
1. Solution SO4
2-
2. Adsorbed SO4
- - Readily available fraction.
3. Insoluble SO4
-
4. Reduced inorganic compounds.

13. • Factors affecting S oxidation (availability) in soils
a. Microbial population in soil.
b. Characteristics of the ‘S’ source
c. Soil environmental condition.
d. Soil micro flora- Chemolithotropic S bacteria Thiobacilli utilized energy from
oxide of inorganic S for the fixation of CO2 in Organic matter.
e. Soil temperature- Rate of S oxidation increases with temperature increase.
Ideal temperature 25 – 40°C.
f. Soil moisture and aeration-S oxidizing bacteria are mostly aerobic and their
activity will decline if O2 is lacking due to H2O logging. Favourable moisture is
field capacity moisture.
g. Soil pH- Optimum pH 4.0 or lower.

15. Dynamics of Sulphur
• Numerous transformations of S in soil occur from inorganic (plutonic rocks) to organic
forms due to the presence of heterotrophic microorganism viz.,. Thiobacillus,
Chlorobium, Desulfo tomaculam and Desulfo vibrio.
• Most of the S remains in organic form and becomes part of soil humus.
• The S supply to plants in largely depend on the SO4
- released from the organic soil
fractions and from the plant and animal residues.
• The nature of applied sulphur is in the form of sulphates of Ca, Mg, K, Na or NH4 in soil
solution in arable soils.
• These sulphates may be adsorbed on 1: 1 clay or hydrous oxides of Fe and AI. It may be
absorbed by plants and microorganisms.
• Sulphates are reduced to sulphides in waterlogged soils and form H2S, FeS etc.
• Elemental sulphur is oxidized to sulphates by microorganisms in aerated soils

17. MICRONUTRIENTS
Essentiality given by,
• Iron (Fe) : E. Greiss (1844)
• Manganese (Mn) : J.S. Hargue (1922)
• Zinc(Zn) : Sommer and Lipman (1926)
• Copper (Cu) : Sommer, Lipman and Mc Kenny (1931)
• Molybdenum (Mo) : Arnon and Stout (1939)
• Sodium (Na) : Brownell and wood (1957)
• Cobalt(Co) : Ahamed and Evans (1959)
• Boron(B) : Warring ton (1923)
• Chlorine (Cl ) :Broyer (1954)
• Nickel :Brown et.al.(1987)

18. FUNCTIONS
• Boron – Vital for reproduction, flowers and fruit formation.
• Chlorine – Helps root growth
• Copper- Enzyme activation
• Iron- Used in Photosynthesis
• Manganese- Chlorophyll component, Enzyme activation
• Zinc- Component of enzymes and auxins
• Molybdenum- Nitrogen Fixation
• Nickel- Nitrogen Liberation
• Cobalt- Nitrogen Fixation
• Silicon- Cell wall toughness

19. UPTAKE FORM & MOBILITY
Mobility in Soil:
The mobile nutrients are highly soluble and are not adsorbed on clay complex;
e.g.: B03
- , Cl- , Mn2
+.
Less mobile nutrients are also soluble, but they are adsorbed on clay complex
and so their mobility is reduced; e.g.: Cu++
Immobile nutrient ions are highly reactive and get fixed in the soil; e.g.: Zn++ .
Mobility in Plants:

20. MICRONUTRIENT DYNAMICS
.

21. • Chelates are soluble organic compounds that bond with metals such as Fe, Zn, Cu
and Mn increasing their solubility and their supply to plant roots.

22. IRON
Sources of iron
• Earth crust contains about 5%
• Primary and secondary minerals such as
• Olivene, Pyrite, Hematite, Goethite, Magrulite, limestone
Forms of iron
Fe occurs in Four major forms in soil. Primary and secondary minerals Fe, Adsorbed Fe,
Organic Fe and Solution Fe
Factors affecting Fe availability
1. Organic matter
2. Interactions with other nutrients
Fe deficiency occur due to the accumulation of Cu, Mn, Zn, Mo and P.
Fe availability decreases when the soils are having more NO3- than NH4+ deficiency of K
or Zn can reduce Fe translocation with in plants.
• Fe is absorbed by plants
roots as Fe2+, Fe3+ and
chelected irons.
• Sufficiency range of Fe in
plant tissue is 50-250
ppm.

23. 3. Soil pH, Bicarbonate and Carbonates
4. Excessive H2O and poor aeration
Fe (OH)3 (Soil) 3H+ Fe3+ + 3H2O
• For every increases in pH, Fe3+ concentration decreases 1000 fold.
• The insoluble Fe3+ form predominates in well drained soils
• Levels of soluble Fe2+ increases significantly when soils become H2O
logged.

25. MANGANESE
Sources of Mn
• Earth crust contains 1000 ppm
• Manganite MnO (OH),Braunite Mn2O3
Forms of Mn
• i. Solution Mn2
+
• ii. Exchange Mn2
+
• iii. Organic bound Mn
• iv. Mn Mineral
Factors affecting Mn availability
• 1. Soil pH and carbonates
• 2. Excessive H O and poor aeration
• 3. Organic matter
• 4. Climatic factor
• 5. Soil micro organism
• Mn2
+ is the available
form
• Mn concentration in
plant ranges from 20 to
500 ppm

27. ZINC
Sources of zinc
• Soil : 10-300 ppm
• Igneous rock : >10 ppm
• Sedimentary : > 95 ppm
Forms of soil Zn
• 1. Solution Zn2
+
• 2. Adsorbed Zn2
+
• 3. Organically completed Zn2
+
Factors affecting Zn availability
• 1. Soil pH : Higher the soil pH, poor aeration greater the Zn deficiency
• 2. Organic matter
• 3. Interaction with other nutrients: SO4 and N can increase the Zn uptake in plants.
• Zn2
+ is the available
form.
• Concentration in
plant 25 to 150 ppm

29. COPPER
Sources of copper
1. Primary minerals- Chalcopyrite, Chalcocite, Bornite
2. Sedimentary minerals- Oxides, Carbonates, Silicates, Sulphates.
Forms of soil copper
• 1. Soil solution - ionic and completed
• 2. Cation exchange sites of clay and organic matter
• 3. Occluded and co-precipitated in soil oxide material.
• 4. Inorganic matter and living organisms
• Copper is absorbed by
plants as cupric ion
Cu2
+
• Normal concentration
in plants 5-20 ppm.

30. Factors affecting Cu availability
• 1. Soil texture- Sandy soils contain lower amounts of Cu than silt and clay
soils.
• 2. pH- Concentration decreases with an increase in pH
• 3. CEC, Org matter content
• 4. Interaction with other elements- Application of NPK fertilizer. High
concentration of Zn, Fe and P in soil solution also can depress Cu absorption.

32. BORON
Sources of boron
• In earth crust igneous rocks (<10 ppm)
• Tourmaline and borosilicate contains B.
Forms of boron (Boron cycle)
1. Rocks and minerals
2. Adsorbed on clay surface, Fe and Al oxides combined with O.M.
3. Boric acid (H3BO3) and 4 B (OH)-4 in soil solution
Factors affecting B availability
• 1. Soil texture : Fine text. soils added B for longer period than coarse text. soils but availability is low.
• 2. Type of clay : Mica > mont > kaolinite
• 3. Soil pH and liming : Less avail to plants with increase pH, heavy liming lead to greater adsorption
and reduced B uptake.
• 4. Interactions with other cations: Occurrence of Ca in alkaline soil with restrict B availability.
Increased K rates causes B toxicity.
• 6. Soil moisture: Restricted moist supply reduce the B availability in the root zone.
• B concentration in plants
varies between 6 and 18
ppm.
• It is absorbed by plants as
undissociated boric acid
(H3BO3).

34. MOLYBDENUM
Sources of Mo
Earth crust 2 ppm : and range from 0.2 to 5 ppm.
Forms of Mo
1. Non exchangeable Mo in primary and secondary minerals.
2. Exchangeable Mo held by Fe and Al oxides.
3. Mo in soil solution
4. Organically bound Mo.
Mo in solution occurs mainly as Mo4=, HMoO4-, H2MoO4o.
Factors affecting Mo availability
• 1. Soil pH and liming- Mo availability increases with increasing pH
• 2. Reaction with Fe and Al- Strongly absorbed by Fe and Al oxides.
• 3. Interaction with other nutrients- Mg and P enhances Mo absorption by plants.
High level SO4, Cu and Mn decrease Mo uptake by plants. NO3- N encourages Mo
uptake, NH4- N reduces Mo uptake

35. CHLORINE
Sources of Cl
• i. Igneous and metamorphic rocks
• ii. Soluble salts such as NaCl, CaCl2 and Mgel2.
• iii. Earth crust 0.02-0.05%.
Forms of Cl
• It is available as Cl- in the soil solution
Availability of Cl
• It is highly mobile in soils.
• It is easily taken by roots
• It is mobile with in the plant it can be rapidly recycled through soil systems.
• But it is prone to leaching.
• Normal concentration in
plant is about 0.2-2.0%.
• Absorbed by plants as Cl-
through roots and aerial
parts.

36. NICKEL
• Nickel content in plant is 0.1 - 1.0 ppm dry matter basis.
• Taken by plant as Ni 2 +
• High levels of Ni may induce Zn or Fe deficiency
1. Ni - metal component of urease that catalyse reaction.
CO (NH 2)2 + H 2 O 2NH3 + CO 2.
2. Essential for N metabolism.
3. Stimulates nodule weight and yield of crops.

37. BENEFICIAL ELEMENTS
SODIUM
Forms of Na in soil
• Solution, exchangeable Na and in silicate minerals.
• In arid and semi arid soils Na exist in silicates, NaCl, Na2SO4
• Na salts accumulating in poorly drained soils of arid and semi arid regions and
causes soil salinity and sodicity.
Effect of Na on soil properties
• Dispersing action of Na+ on clay and organic matter reduces soil aggregation,
permeability to air and H2O, germination and root growth.

38. VANADIUM
• Low concentration of Vanadium is beneficial for growth of Microorganisms.
• Vanadium substitute for Mo in N fixation by Rhizobia.
• Involves in Biological - oxidation-reduction reactions.
COBALT
• Normal concentration of Co in dry matter - 0.02 - 0.5 ppm.
Factors affecting : Co availability
• 1. Soil pH : Avail increase with increase in soil acidity, H2O logging conditions.
• 2. Liming and drainage practices - reduce co availability.
• 3. Application CoSO4 rectify the deficiency.

39. SILICA
Sources of silicon
• Earth crust : 27.6% Most abundant element in earth crust.
• Soils 23-35%
• Primary and secondary mineral and quartz - major source.
• Quartz is the most common mineral in soil, comprising 90-95% of all sand and silt fractions.
Factors affecting Si availability
• 1. High H2O content encourages Si uptake
• 2. Heavy application of N decreases Si concentration
• 3. Liming decreases Si uptake in plants.
• 4. Acidification increases Si uptake
• 5. Fe and Al oxides influence Uptake of Si by plants.

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